As for the supposed masses of peaceful, tolerant Muslims who don't support this sort of idiocy, they ought to speak up.
Imagine if every time Fred Phelps contracted a new case of diarrhea of the mouth, it was on international TV, and no Christian contradicted it. Imagine further that he had established religious schools, many with state funding, to espouse his views. Make one more stretch and imagine that roughly half of the baptist churches in the country were also in complete accordance. Would the rest of the world not think that Fred Phelps' version of Baptist Christianity was what all American Christians believed? Would we not also, as a society, be to blame for not speaking out against Phelps' drivel?